Halogen incandescent lamps customarily have a bulb or envelope of hard glass or quartz glass, within which a coiled incandescent filament is located. The coiled incandescent filament may have portions or sections thereof which are straight, that is, not coiled. A mount is enclosed in the bulb or envelope, which has at least two inner current supply leads. The current supply leads typically are of molybdenum, and are connected to outside terminals over molybdenum foils or the like, sealed in a press or pinch seal closing off the bulb. The filament may be a coiled or a double-twist filament. It is usually made of tungsten wire.
It has been found that mount components made of molybdenum decrease the lifetime of halogen incandescent lamps due to problems which arise in connection with the halogen cycle. To reduce such problems, it has been proposed to make the inner metallic components, especially the current supply leads, of tungsten. Tungsten is very brittle, and it has been found effectively impossible to insure a reliable mechanical connection as well as an excellent electrical terminal connection between current supply leads and the filament by a clamp or compressed sleeve connection. Such clamp connections can be used, however, with molybdenum leads, since molybdenum is substantially less brittle than tungsten--see German Patent Disclosure Document DE-OS No. 21 26 796.
It has also been proposed to slip the end of the coiled incandescent filament on the current supply lead wire. The diameter of the current supply lead wire is selected to be slightly smaller than the inner diameter of the coil forming the filament. Mechanical retention, as well as electrical connection of such an arrangement, is not reliable, however, and may lead to intermittent terminal connections. This makes it especially difficult to connect halogen cycle incandescent lamps in a dimmer circuit, and to dim the output of the filament. The capability to dim incandescent lamps makes them especially suitable for many applications and is desirable for many uses.
It has been suggested to hot-crimp or bend the current supply leads in advance of slipping the coil of the coiled filament thereover, in order to obtain, for example a hanger connection. U.S. Pat. No. 3,930,177 describes such an arrangement in which the filament coil is placed over a bent-out end portion of a support wire forming a current lead-in. Such arrangement contributes substantially to production time and costs, and also cannot be readily automated on production machinery. In spite of such efforts, the terminal contact between the coiled filament and the tungsten lead-in wire was not improved to result in an entirely satisfactory electrical and mechanical connection.